Excellent statement from the leadership at UW Madison, which explains what "indirect" expenses are very well

Here; an excerpt:

As part of how the government provides funding, and how it has done so for decades, federal agencies like the NIH – most typically through highly competitive grant processes – allocate funding to individual projects and institutions. This funding supports direct expenses like staff salaries, graduate student stipends, and supplies. It also supports indirect costs, which include everything from large, shared scientific equipment, to laboratory and facility construction costs, data infrastructure costs, utilities, the costs of administering grants appropriately and the often-considerable expense of complying with federal rules and regulations surrounding research.

These so-called “indirect costs” aren’t optional expenses. They are both substantial and an absolutely fundamental part of innovative science. As is the case while running your household, you need both money to buy groceries (direct) and the financial resources to keep a working refrigerator and electricity (indirect) to store your milk and eggs.